A cable modem network or “cable plant” employs cable modems, which are an improvement over conventional PC data modems and provide high speed connectivity. Digital data on upstream and downstream channels of the cable network is carried over radio frequency (“RF”) carrier signals. Cable modems convert digital data to a modulated RF signal for upstream transmission and demodulate a downstream RF signal to bit streams for use by computers. The conversion is done at a subscriber's home. At a cable modem termination system (“CMTS”) located at a head end of the cable network, the conversions are reversed. The CMTS converts downstream digital data to a modulated RF signal, which is carried over the fiber and coaxial lines to the subscriber premises. On the return path, the CMTS receives the modulated upstream RF signal, which it demodulates and transmits to an external node. A current standard for transmission of data over cable networks is the Data-Over-Cable Service Interface Specification (“DOCSIS”).
In earlier cable networks, there was no provision for any redundancy at the CMTS. Without redundancy, a failure of the one of the CMTS resulted in a service disruption or service outage of the cable modems relying upon the failed element. In such networks, the failed CMTS had to be repaired or replaced before service could resume. This meant that service could be out for an extended period. From the perspective of the service provider and the end user, any type of disruption or delay in service is extremely undesirable.
In a known system, an N+1 redundancy technique employs at least two CMTS interfaces (e.g., line cards) on one or more CMTS chassis at the head end of a cable network. One of the CMTSs serves as a backup or “protecting” CMTS. When another CMTS (a “working” CMTS) becomes unavailable to service its group of cable modems, the protecting CMTS takes over service to those cable modems. The protecting CMTS provides service on the same downstream and upstream channels as used by the working CMTS.
In load balancing, cable modems are moved among upstream and downstream channels after their initial registration and coming online while potentially passing traffic. Cable modems that are currently online are moved when the load difference between two interfaces exceeds a user-defined percentage. In this way, service providers are allowed to optimally use both downstream and upstream bandwidth, enabling the deployment of new, high-speed services such as voice and video services. Additionally, load balancing may help reduce network congestion due to the uneven distribution of cable modems across the cable network and due to different usage patterns of individual customers. Load balancing may be enhanced and supported by implementing the Dynamic Channel Change (DCC) protocol primitive.